In the glamorous world of the 1960s grand tourer, Italy and England reigned supreme; that was until Peter Monteverdi crashed heavily in Formula One and turned his tenacity to building a Swiss competitor...

Citroen destroyed its SM V8 prototype when De Tomaso took over. So one enthusiast built his own - with the original engine.

Everyone who is vaguely interested in motoring loves Citroens but very few of us actually have the courage to own one. That's unfair, because early Citroens, such as the Traction Avant and the 2CV, were as tough as anycar. But with the arrival of the DS, Citroen came over all avant-garde and, although it was powered by cheap and simple engines, the hydropneumatic suspension and brake system frightened off owners in the days when many people actually serviced cars themselves. The DS was superbly French but rather too idiosyncratic for most.

The fabulously outrageous SM was the same, only more so. Styled by Robert Opron and fitted with a Maserati V6 engine, along with the signature hydropneumatic suspension and brake system that Citroen doggedly stuck to, the SM was an exotic-looking creation. Unfortunately it was launched when the automotive industry – especially in France – was in chaos, the fuel crisis was about to hit and the car proved to be underdeveloped and unreliable.

During the decades since, the SM was largely ignored by the mainstream classic car world, seen as an over-complicated underachiever. For years, old SMs could be seen smoking around less salubrious suburbs with bits of fragile trim hanging off and the brittle interior crumbling. But in the last few years prices have jumped as the SM has become a desirable icon of the 1970s. With specialists such as Garage Daunat and Regembeau in France and Andrew Brodie in the UK proving that SMs can be made to run reliably and their foibles remedied, interest has rocketed. Even Octane editor David Lillywhite is in the process of importing one!

The SM was recently afforded a seven- page feature in Octane (issue 89), so this is not the place to repeat all the history. And nor should it be, because the car we have here is not one of the ordinary 12,920 production models but a replica of a one-off prototype. In fact it’s the only Citroen SM V8 in existence.

To the bafflement of many, Citroen purchased Maserati in 1968 and this gave it access to Maserati’s engine department, headed by Giulio Alfieri who developed the 2.7-liter V6 for the SM. According to marque expert Marc Sonnery, and detailed in his upcoming book Maserati and Citroen Years 1968-1975, in the spring of 1974 Alfieri was tasked with developing a new V8 engine for the Maserati Quattroporte II. The old Indy/Bora V8 was deemed too heavy and out of date so the Merak V6 engine was the basis for a fresh and more efficient 4.0-liter V8, and the idea was to test it in an SM.

Alfieri ingeniously enlarged the V6 by cutting it in the middle of the third cylinder from the front and mating it with a one-and-a-half cylinder section from another block. Perfecto! A lightweight V8 that sits behind the front-wheel-drive SM's gearbox.

Marc Sonnery put the question to Cleto Grandi, who was head of tecnico in the late Alfieri’s R&D department for Maserati, and he says: ‘Since Mr Malleret [director of Maserati for Citroen] did not want to use the traditional V8, judged too long in the tooth and uneconomical, it was decided to make a Merak Plus 2 engine… we took a Merak block and welded two additional cylinders from another Merak block and this engine came together quite simply.’

Grandi continues: ‘It was installed in the same position as the six-cylinder except that, to make room for the two additional cylinders, we had to modify the bodyshell slightly in the area of the dashboard to be able to fit the coolant pipes.’

The gearbox remained standard, as Grandi explains: ‘Normal five-speed gearbox, yes. We practically did not change a thing… To be able to fit [the engine] in the car, we flattened, as opposed to cut, the firewall and it just fitted in. There wasn’t a lot of spare space, however.’

One of Citroen’s reasons for purchasing Maserati was because of the smaller company’s ability to produce prototypes quickly and Alfieri’s engineers were skilled at aluminium welding. Grandi says: ‘The distributor, we obviously took one for a V8, I am sure we fitted a Bosch unit, and we made longer camshafts and crank. The most difficult part of the job was to cut the two engine blocks and then afterwards weld them on the inside. That was difficult because of water and oil flow… you have all these passageways which had to be machined and then the two parts of the V8 were placed together so that everything could be calculated, then a welding tool specifically made for aluminium managed to weld it all very well.’

The compact V8 was secreted into the SM’s engine bay using the standard gearbox and engine mounts, with the firewall ‘tapped with a hammer’ – as Grandi tactfully puts it – to accommodate the extra cylinders. The regular SM sound-deadening material had to be removed, the exhaust manifolds took a bit of work, and additional pipes had to be added to both headers at the correct angle.

The standard SM chosen to take the prototype V8 was finished in Rio Red with a black interior – exactly like you see in these photographs. ‘Ingegnere Alfieri (and others) did about 12,000km with the car, using it not only as a test bed but also for his personal commute home,’ says Grandi. ‘There was troppo potenza [too much power] so we had to change the suspension settings. Then at the end of the testing and development stage we removed the engine and, as the car was by then in poor condition, it was dismantled and scrapped.’

By 1975 Michelin had decided to sell CitroΫn to Peugeot along with Maserati, which was haemorrhaging money. Peugeot then sold Maserati to Argentinean industrialist and ex-racing driver Alejandro de Tomaso. A fiery character, he wanted all signs of CitroΫn totally expunged from Maserati’s history and the SM V8 was one of the casualties.

Although the original Rio Red SM bodyshell was crushed, the special engine was saved along with other important Maseratis, including a collection of historic racingcars. This collection was then preserved by the Panini family in Modena, where it was put on display at its Parmigiano cheese factory. In 1998 the SM V8 engine was sold to the German Maserati collector Hermann Postert, who displayed it on a stand in his home.

In the summer of 2009, private collector Philip Kantor persuaded Postert to sell him the prototype engine, to realise a long-held ambition. ‘My late father loved SMs,’ says Kantor. ‘The trouble was they proved somewhat unreliable so he owned five at once to ensure one would always be running. He thought the cars were great but underpowered. Discovering that Alfieri had created this one-off prototype V8, and researching exactly how he had gone about it, I knew I had to recreate it, using the original V8 engine. My father would have really appreciated the engineering challenge and most certainly the result.'

Citroen SM specialist Frederic Daunat was entrusted with this personal project and recreated the V8 in accordance with the original prototype. And now Octane gets the chance to drive this unique SM in the quiet rural surrounds of Herbeville, near Versailles.

It's immaculately finished in the soft orangey hue that is Rio Red, wearing the rare composite wheels made by Michelin, and its smart black leather interior appears original. In fact, the SM V8 looks no different to a regular SM but, when the engine fires, the cat is out of the bag.

And, mon dieu, it sounds good! There’s a very angry Italianate rasp that promises a good deal of power. It was never dyno’d, but the 4.0-liter V8 is thought to be whacking out around 260bhp.

The driver’s seat is big and soft; the view over the curved dash and fat steering wheel clear. The clutch operates as it would in the V6 and the V8 provides plenty of shove off the line, while the gearshift moves around the heavily chromed gate beautifully. That fat steering wheel needs to be so because you really have to hang onto it – with high gearing and extremely strong self-centring, you cannot palm along with one hand.

Frederic Daunat, who prepares rally-winning SMs, has beefed up the hydropneumatic suspension but the car retains that incredible gliding ability across the country roads. As instructed, the brake button on the floorboard has to be treated very gently and at first application the SM nosedives to a very sudden halt. It takes practice to learn how to toe it correctly and it is a bit disconcerting not having a brake pedal to feather into blind bends, but at least you are always assured that the 1450kg Citroen will stop.

But going, not stopping, is this car’s intention and, boy, is it quick. The V8 engine note hardens at about three thou', then goes off the chart with enthusiasm. Minimal sound deadening means you hear it at work from inside, and what a wonderful sound. With super-sharp steering, immense brakes, a tautened chassis and a fabulous V8, this prototype replica is the car that the SM always should have been. It’s fast, comfortable, totally sorted, and the added power allows you really to exploit the capable chassis and benign handling to the full. This impressive Citroen is exactly what the late Mr Kantor Sr would have enjoyed for his high-speed European motoring.